The following points highlight the nine main factors affecting ripening of sugarcane. The factors are: 1. Location 2. Low Temperature 3. High Temperature 4. Varieties 5. Fertilisers 6. Intercropping 7. Irrigation 8. Lodging 9. Flowering.
Factor # 1. Location:
Analysis of cane juice quality in cane growing countries has revealed that the two outer one- third belts of tropics (regions between 16° and 21°, both N and S of equation) are, generally, characterised by higher juice qualities than the other regions. In the equatorial zone, temperatures show little variation.
In the regions beyond the Tropics of Cancer and Capricon, winter temperatures go down too low and this affects cane quality and ripening adversely. In India, in general, subtropical zone is characterised by a narrow period of peak recovery whereas the southern area although giving poor recovery has a longer spread.
Factor # 2. Low Temperature:
North Indian plains have the advantage of a cool, dry weather following the hot humid rainy season. Bihar climate has good juice quality as its climate is much favourable for cane ripening. However, in central and western parts of north Indian plains (Lucknow-Sitapur to Amritsar-Jalandhar), the favourable season is vitiated by the weather becoming too cold in mid-winter.
Ripening is fast during October and November but when temperatures drop to the shivering stage, the ripening rate slows down and maturation come to a standstill. During the coldest period of December and January, the quality actually drops down by one-half to one-whole unit or more, the colder the spell the deeper the fall.
Maximum temperatures between 23° and 32°C and minimum between 7° and 14°C are favourable to a steady rise in juice quality. Deterioration in quality sets in when maximum temperatures come down between 7° and 13°C and the minimum below 3°C.
Factor # 3. High Temperature:
After the cold spell, juice quality in terms of sugar content and purity begins to rise once again. In February-March, when peak maturity is attained, the quality as a whole more or less levels off for 10-20 days.
When hot weather sets in May, juice quality usually starts to go down. In many parts of India, this is because of extreme heat and drought, with no irrigation, the standing cane stalk deteriorates. If irrigation is given, cane stalk may resume growth.
Factor # 4. Varieties:
Early varieties (Co 8336, Co 8337, Co 8339, Co 8340, Co 8341, CoS 8436, CoJ 64 and CoC 671) attain a given level of sugar content and purity at an earlier period in crushing season than the late ripening varieties. January-February planted crop will have higher juice quality compared to May planted crop. Autumn crop give better purity than sprig crop throughout the season.
Factor # 5. Fertilisers:
Excessive and late application of nitrogen fertilisers delay ripening. Hence, such fertilisers should be applied within first two or three months of planting. In October planted crop, fertiliser application should be completed before March. Phosphate deficient soils are known to produce cane of low sucrose content. Potassic fertilisers increase extraction per cent juice from cane.
Factor # 6. Intercropping:
Intercropping in October or July planted crop improve juice quality probably due to restricted late tillering of cane. Further, intercropping is usually practiced in autumn planted cane because during winter, growth of cane crop is lesser and hence it is not seriously affected by the competition. Intercropping in February planted crop, however, has adverse effect on juice quality.
Factor # 7. Irrigation:
Irrigation, by favouring early growth, leaf development and stalk formation lengthens the period of effective growth resulting in higher potential for sugar formation and storage. Thus, irrigations have beneficial effect on juice quality.
Post-monsoon irrigations, particularly after mid-November may not improve juice quality in areas where temperatures are too cold as in parts of north India. In tropical India, where the weather remains warmer, irrigations after rainy season have a definite advantage on sugar formation.
In tropical India, where mean temperatures in winter are around 30°C, post-monsoon irrigations cause continued growth leading to slow ripening. To improve ripening in such areas, regulated irrigations are practiced.
The crop is subjected to a gradually increasing, but moderate drought situation. Such regulated irrigation forces the cane to ripen without significant loss in yield. The gradually imposed drought retards the growth and elongation of internodes and favour sugar accumulation.
Factor # 8. Lodging:
Strong winds accompanied by heavy rainfall during September-October cause lodging of the cane crop. Even the inclination of stalk causes proportionate reduction in sucrose and purity of its juice. When the stalks are laid flat, the deterioration is more. Earthing up and propping can minimise the lodging by keeping the cane erect.
Factor # 9. Flowering:
In sugarcane, flowering often takes place when the crop also starts ripening. Many consider that flowering is a sign of ripening. This is, however, not true since some of the varieties, especially in Karnataka flower during October at which time it can hardly be considered mature.
In the early period of flowering, perceptible changes in sugar content are not observed except a little improvement. The adverse effect of flowering on juice quality comes at the time of seed setting within the flower and afterwards. The top portion of the flowered cane becomes pithy and dry with some side shooting. Sugar content of that part of the plant thus is adversely affected.
The results of experiments, however, have been inconsistent on this aspect probably because different workers have analysed the flowered and un-flowered canes at different stages. Secondly, flowered and unflowered canes are of different age groups, thus their maturity schedules also differ. Prevention of flowering by appropriate techniques combined with artificial ripening may help to increase the yield and juice quality of cane.